It had like an %80 kill ratio for strays, and took out any of our weaker animals (those with feline
AIDS, for example FLS). This does sound like that. It happened so quickly we didn't even have time to get to a vet before it had mostly run it's course.
The problem is the secondary infections, which you try to treat with antibiotics. But the other big problem is a cat with a stuffed up nose WON'T EAT. They can't smell their food, and feel sick, so they have no real appetite.